A cell connector to connect a plurality of galvanic cells, a system and a method to connect a plurality of galvanic cells are essentially known from the prior art. It is known to connect galvanic cells in series and/or parallel in order to achieve a total voltage that exceeds the voltage of an individual cell and/or to achieve a total current that exceeds the current of an individual cell.
In particular, in the case of high packing densities, as is the case by way of example in the case of accumulators or rather batteries for vehicles, it is problematic to electrically connect the individual cells. On the one hand, the connecting surface is relatively large owing to the high currents in batteries of this type; on the other hand, the space between the cells for arranging a tool to connect the cells is relatively small.
Accumulators of this type are frequently constructed with the aid of so-called “pouch cells.” The housing of a pouch cell is not rigid but rather flexible and is based by way of example on a pouch that is produced from aluminium foil. The actual cells are located welded in this foil and have terminal tabs that are guided to the exterior and in most cases the terminal tabs comprise a longitudinal form. While connecting the pouch cells, the terminal tabs are attached by way of example by ways of laser welding or ultrasonic welding. Various module head embodiments and attachment methods are known for this purpose.
By way of example, German Patent Publication No. DE 10 2010 008 582 Al, WO 2013/000889 Al and U.S. Patent Publication No. 2010/0190055 Al respectively disclose accumulators that are constructed from stacked individual cells and whose connecting lugs are connected with the aid of cell connectors. DE 10 2010 008 582 Al specifically describes a method in which the connection terminal stack is pressed together with the aid of an air current. In U.S. Patent Publication No. 2010/0190055 A1, the terminal tabs of the individual cells are connected to one another with the aid of U-shaped cell connectors.
In general, thin-walled pouch cells with a thickness of less than approximately 7 mm are currently only cost-effectively produced by ways of laser welding methods if the pouch cell-to-pouch cell spacing may not be increased. In the case of pouch cells that are more than approximately 7 mm thick, the ultrasonic welding method may also be used. However, the joining area that may be produced in one working step is limited to 25 mm2 so that it is necessary to weld a terminal tab in general in a plurality of working steps, in order to achieve the necessary current cross section, but also to ensure a cost-effective portable tool service life of the ultrasonic welding head. The proposed numerical values are of course only to be understood as approximate values to illustrate the problem in accordance with the invention, they are not, however, used to categorically rule out a joining method for specific application cases.
In general, an ultrasonic welding tool should be embodied in a relatively solid manner to ensure good thermal dissipation properties. The forces that are to be applied and vibrations that occur require a robust construction. This is set against the fact that it is not possible to embody the anvil and the sonotrode of an ultrasonic welding tool in an arbitrarily solid manner owing to the cell density and consequently owing to the limited accessibility to the terminal tabs of the cells.